The present invention relates to disc drive data storage systems and, more particularly, to a disc drive data storage system having a slider with steps approximating a leading taper.
Disc drives of the xe2x80x9cWinchesterxe2x80x9d type are well known in the industry. Such drives use rigid discs which are coated with a magnetizable medium for storage of digital information in a plurality of circular, concentric data tracks. The discs are mounted on a spindle motor which causes the discs to spin and the surfaces of the discs to pass under respective hydrodynamic (e.g. air) bearing disc head sliders. The sliders carry transducers which write information to and read information from the disc surfaces.
An actuator mechanism moves the sliders from track-to-track across the surfaces of the discs under control of electronic circuitry. The actuator mechanism includes a track accessing arm and a suspension for each head gimbal assembly. The suspension includes a load beam and a gimbal. The load beam provides a load force which forces the slider toward the disc surface. The gimbal is positioned between the slider and the load beam, or is integrated in the load beam, to provide a resilient connection that allows the slider to pitch and roll while following the topography of the disc.
The slider includes an air bearing surface which faces the disc surface. As the disc rotates, the disc drags air under the slider and along the air bearing surface in a direction approximately parallel to the tangential velocity of the disc. As the air passes beneath the air bearing surface, air compression along the air flow path causes the air pressure between the disc and the air bearing surface to increase which creates a hydrodynamic lifting force that counteracts the load force and causes the slider to lift and fly above or in close proximity to the disc surface.
One type of slider is a xe2x80x9cself-loadingxe2x80x9d air bearing slider, which includes a leading taper, a pair of raised side rails, a cross rail and a subambient pressure cavity. The leading taper is lapped onto the end of the slider that is opposite to the recording head. The leading taper pressurizes the air as the air is dragged under the slider by the disc surface. An additional effect of the leading taper is that the pressure distribution under the slider has a peak near the taper end or xe2x80x9cleading edgexe2x80x9d due to a high compression angle of the taper, and a second peak near the recording end or xe2x80x9ctrailing edgexe2x80x9d due to a low bearing clearance required for efficient magnetic recording. This dual-peak pressure distribution results in an air bearing with a high pitch stiffness.
The bearing clearance between the slider and the disc surface at the recording head is an important parameter to disc drive performance. It is desired to minimize variation in the head clearance or xe2x80x9cflying heightxe2x80x9d. Therefore, it is important to control several metrics of flying height performance, such as flying height sensitivity to process variations, ambient pressure (e.g., altitude) variations, changes in radial position of the slider over the disc surface and resulting head skew, and quick movements of the slider from one radial position to another radial position. Also, the slider should take off from the disc surface as quickly as possible after the start of disc rotation.
The above-mentioned sensitivities are reduced by providing the slider with a high bearing stiffness in the pitch and roll directions and vertically in a direction normal to the disc surface. High vertical bearing stiffness has been achieved with the use of sub-ambient pressure cavities. The cross rail provides an expansion path for the air to de-pressurize as it is dragged into the sub-ambient pressure cavity by the disc velocity. The expanded air in the cavity provides a self-loading force which forces the slider toward the disc surface. The counteraction between positive pressure developed along the side rails, the preload force provided by the suspension and the self-loading force provides the air bearing with a high vertical stiffness and a relative insensitivity to variations in ambient pressure. To achieve high pitch and roll stiffness, air bearings have utilized geometries that distribute the positive pressure away from the center of the slider.
Quick take-off is typically achieved by developing high pressure near the leading edge of the slider through the leading taper. The leading taper causes the pressure to rise rapidly from ambient pressure at the slider""s perimeter towards the interior of the slider. This rapid pressurization is also useful in improving pitch and normal stiffness and in decreasing changes in fly height with changes in ambient pressure.
Since the air bearing surface is pressurized by the leading taper, variation in the taper angle and the position of the taper relative to other air bearing surface features causes the flying height of the transducer to vary. In addition, the flying height of the transducer typically varies proportionately more with variations in the manufacture of the taper than with other manufacturing variations.
There are three major difficulties associated with the conventional method of forming the leading taper. First, the angle of the taper with respect. to the air bearing surface can be controlled only to the degree afforded by the mechanical tilting mechanism used during the grinding or lapping process. Second, the length of the taper and its position with respect to other air bearing surface features varies with the uncertainty in the grinding or lapping rate and with the tilt angle. The intersection between the leading taper and the air bearing surface has the greatest variability in location relative to other air bearing surface features, at shallow taper angles. Third, conventional grinding or lapping processes permit only linear leading tapers. Also, the intersection between the taper and the air bearing surface is limited to a line which is parallel to the trailing edge of the slider.
Alternatively, sliders have been fabricated with a step at the leading edges of the side rails. This leading edge step constrains air flow approaching the side rails and causes the pressure to increase substantially when the flow reaches the rails. Leading edge steps are typically fabricated by ion milling the bearing surface. With ion milling, the position and depth of the step can be controlled very accurately. However, a leading edge step does not pressurize the leading edge of the slider as effectively as a leading taper.
Improved slider geometries are desired which effectively pressurize the leading edge of the slider and yet have small flying height sensitivities to process variations and ambient pressure.
One aspect of the present invention relates to a self-loading disc head slider having a slider body, with a leading slider edge and a trailing slider edge, and first and second raised rails. Each raised rail has a leading rail edge, inside and outside rail edges and a bearing surface. A cavity dam extends between the first and second raised rails. A subambient pressure cavity trails the cavity dam, between the first and second raised rails. A stepped leading taper extends from the leading slider edge to the bearing surfaces of the first and second raised rails. The stepped leading taper is formed of first and second steps. The first step is positioned along the leading slider edge. The second step wraps around the leading rail edges of the first and second raised rails and extends along a portion of the inside and outside rail edges of the first and second raised rails. The first and second steps have a step height of 0.05 to 1.5 microns.
Another aspect of the present invention relates to a disc drive assembly, which includes a housing, a data storage disc, an actuator assembly attached to the housing, a suspension supported by the actuator assembly, and a slider supported by the actuator assembly. The slider has a bearing surface and means for approximating a taper at a leading edge of the bearing surface.